Whenever the Supervolcano under Yellowstone Nat’l Park goes off it will be beyond castrophic, 8,000x as much ash and lava as Mt. St. Helens. Hopefully it won’t happen for at least a few thousand years more, and maybe humans will have some way of dealing better with the aftermath:
http://dsc.discovery.com/convergence/supervolcano/under/under.html
Even the eruptions at Yellowstone pale in comparison with Toba.
Two hundred billion tons of sulphur dioxide alone.
Worldwide, the temperature plummeted 5-10 degrees Fahrenheit, spawning a mini ice age that lasted a thousand years.
Except for the 2-5 thousand humans who survived, we wouldn’t be here.
From the maps I’ve seen Denver is right on the border of the kill zone from a Yellowstone eruption. I hope it won’t be a few thousand more years!